The pound fell to its weakest level against the Singapore dollar since Aug 16 after Britain's Prime Minister Theresa May set a timetable for leaving the European Union.

But businesses here warmed to the clarity offered by her announcement that Britain will take the first formal step towards leaving the EU by March next year after June's Brexit vote.

The pound fell 0.6 per cent to S$1.757 at 6.40pm. It was the pound's weakest level since Aug 16, when it hit S$1.736 - its lowest in more than 30 years. The pound also hit a seven-week low against other major currencies.

The fall came despite Purchasing Managers' Index data showing British factories had their best month in over two years in September.

Mr Nizam Idris, head of forex strategy at Macquarie Bank, noted the positive data but said that data tends to be backward-looking, in contrast to the currency markets.

"It's going to be a slow grind for the sterling," he said. "The hope was that despite Brexit, the leaders (would be) able... to maintain the status quo, but that doesn't seem to be the case. The fear of a hard Brexit means significant changes to businesses and that should argue for a weaker sterling."

He forecast a further 6 per cent fall in sterling against the Singdollar by early next year, adding that the fall was an important "first hint". He said: "The first part of the structural change was priced in after the result. The second structural change will depend on how negotiations are conducted. "

But lawyers, economists and business leaders were enthused by the clarity of the timeline.

CIMB Private Bank economist Song Seng Wun said the increased clarity gave a positive sentiment to the market. "At least businesses can plan towards that two-year period from when Article 50 is triggered. From a business standpoint... anything which clears the uncertainty even a bit will help."

Singapore would gain marginally as an external-dependent economy, he added.

Dr Bicky Bhangu, president of the British Chamber of Commerce, said the news would give firms impetus to act: "We anticipate our member companies to begin to finalise their plans for the future."

Although Mrs May has said she will invoke Article 50 by March, she also promised to control immigration while retaining access to the single market, leading to speculation of a "hard Brexit".